Thirty three with mild to moderate Alzheimer's disease (AD) patients (diagnosis of probable AD according to the criteria of the National Institute of Neurological and Communicative Disorders and Stroke Alzheimer Disease and Related Disorders Association [NINCDS-ADRDA] were included in this study) were randomly classified into one of three groups (eleven for each group). The first group received anodal tDCS over left DLPFC and 2rd group received cathodal tDCS on the left DLPFC and the 3rd group received sham tDCS stimulation, daily for 10 consecutive days (5 days/week for 2 weeks). Minimental State Examination (MMSE), psychometric assessment for cognitive functions (MMSE, Wechsler memory scale, Wechsler adult Intelligent scale) were assessed before, after 10th sessions, and then after 1 and 2 month. Cortical excitability was assessed in both hemispheres before and after the end of sessions. Neurophysiological evaluations included resting and active motor threshold (rMT and aMT), and cortical silent period (CSP).